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How do you visually identify aircraft from the ground?
Are there any good resources that teach you how to identify jetliners from the ground? I'd love to see some great comparative photos of their silhouettes. Books or websites are both ok.
For example, here's a plane that was flying over yesterday en-route to KSFO. I'm guessing it's a 747 or A380, but I can't easily guess from this angle.

given the tail and what has been said here I would say that's a 747

not just the tail, the shape of the wing, the diameter of the engines, all indicate a 747 and an early model at that.

The canonical reference for aircraft recognition would be Jane's All the World's Aircraft.
http://www.airliners.net is also a useful resource, but generally means working from photos - the line drawings in Jane's are often easier to use because they abstract away things like airline liveries and distill the aircraft down to its basic shapes.

@JeffreyBosboom Looks like IHS is "restructuring" (breaking every link on) their website. Moved the link to Wikipedia for now.

A Field Guide to Airplanes is also really good. I find it better than Jane's Aircraft Recognition Guide because it is categorized by aircraft appearance, and also is written like a field guide as opposed to a reference book.


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How does altitude affect the speed of sound?
I read once that the speed of sound decreases as altitude increases.  I wonder if that's true and, if so, are the pressure waves made at high altitude lesser than the ones at low altitude because of the difference in air pressure?  And, lastly, does that mean that lower speeds at higher altitudes will be subject to the problems one encounters when approaching mach speed?

See graph from Wikipedia article

I read once that Mach speed decreases as altitude increases.

The speed of sound is solely dependant on temperature.
$$
M = \sqrt{\gamma RT}
$$
where $\gamma$ is the ratio of specific heats, $R$ is the molar gas constant and $T$ is the temprature in Kelvin. For Earth's athmosphere at 15° Celsius,
$$
M=\sqrt{1.4\times 287\times 288.15}=340\,\text{m}/\text{s}
$$
Does temprature decrease with altitude? Well, not always as can be seen by the international standard atmosphere:

(source: cam.ac.uk)

....are the pressure waves made at high altitude lesser than the ones at
  low altitude because of the difference in air pressure?

There is no simple answer to this. Here's NASA's opinion:

Altitude determines the distance shock waves travel before reaching
  the ground, and this has the most significant effect on intensity. As
  the shock cone gets wider, and it moves outward and downward, its
  strength is reduced. Generally, the higher the aircraft, the greater
  the distance the shock wave must travel, reducing the intensity of the
  sonic boom. Of all the factors influencing sonic booms, increasing
  altitude is the most effective method of reducing sonic boom
  intensity.

I edited the question a bit to make it more concise, hopefully it makes it a bit easier to answer...  Also, I'm a little surprised, air density really has nothing to do with the speed of sound?

@JayCarr yep, even nasa says so :) https://www.grc.nasa.gov/www/k-12/airplane/Images/sound.gif

@JayCarr only if you use the gas equation to substitute temperature with density and pressure :P

@JanHudec I wouldn't say difficult, $p=\rho RT$ is one of the primitive equations we use to model the atmosphere.

And humidity? @MikeFoxtrot if the speed of sound depends also on the type of medium, wouldn't a different amount of humidity be a different medium?

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What is the service cycle or interval of the Landing gear of an A380 and 747-8
What is the service cycle or interval of the Landing gear of an A380 and 747-8, i.e how long between service, eg after how many take offs and landings with particular reference to bearing checks and lubrication of the bearings and axles of the wheels

I'm guessing that this is something done at A or B checks, not at a particular landing/cycle interval.

Certainly not less than C check, 4000 to 6000 hours depending on the airplane. Airliners only have minor maintenance and inspections (1A, 2A, 3A, etc. - A checks are 500 hours give or take) that can be done on overnights, until C check which is the first time a lot of panels are removed and components get major servicing and functional testing and the plane is down for a week or so.  A task like that could also be based on flight cycles and if not set at a level that allows coordination with C check down time, becomes "out of phase" maintenance and is a pain in the butt for the airline

20 wheels and 16 wheels respectively for these two aircrafts on their main landing gears do seem to provide a distributed wait per wheel in the same range as on other aircrafts such as the B777 or the A330. I would say the same maintenance interval as other large aircrafts.

https://www.iata.org/whatwedo/workgroups/Documents/MCC-2015-MIA/D2_0945-1030_-Fin_Impact_of_Extending_or_Reducing_Lease_Term-_Joost_Groenenboom.pdf seems to suggest 10 yearly landing gear shop visits for typical operations for both narrow- and widebodies.

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What advantages would a triangular shaped spy plane have over a an SR-71?
This is a picture of the supposed SR-72 Aurora. What kind of advantages would this have over the SR-71, in terms of its triangle design? Paper airplanes have the same shape, and fly really well.

The SR-71 design that I am comparing it to.

Please no negativity. A triangle design is something pretty new the only time an aircraft was built triangle was by Germany during ww2 and I don't believe it actually was in service. With this new design of triangular if it exists or not hat aerodynamic advantages come with a triangle design like the sr-72.For those of you who don't believe NASA actually said they are building an sr-72 spy jst like the one I provided in the picture (https://www.flightglobal.com/news/articles/nasa-launches-study-for-skunk-works-sr-72-concept-407222/)

Paper airplanes have the same shape, but do not fly well They fly very well.  What makes you think this?

@Simon  the ones I build don't fly well. I did make a recent one that had the top of the wing bent down and it had lots of lift (the only successful one I have made) so you are right the fly pretty will. I will edit the question.

The only reason they don't fly for long is because the only thrust they have is the initial throw.  Since they generate drag, as does anything creating lift, but have no thrust, they slow down and can no longer produce enough lift to keep them flying.  Because they have very thin wings and fuselage, they fly very effectively.

triangle design is something pretty new - nope, that's just a delta wing - the most pure form you can get, really. Avro Vulcan, Handley Page HP.115,  Convair F-102 & F-106, Boeing X-32... there are triangular planforms everywhere.

Note that until 2013, the existence of a SR-71's succcessor was pure speculation. Even though, Aurora's shape (and perhaps existence) is still speculation

The 'triangle' wing design that you refer to is pretty common. It is called the delta wing design and is used in a number of high speed aircraft, for example, the North American XB70 Valkyrie.

In fact, the SR 71 wing planform is also a delta, if one removes the engines. One of the reasons is that the wings of the aircrafts are kept inside the Mach cone formed by the aircraft. The Mach angle is given by,
$\mu = sin^{-1} \frac{1}{M}$,
where M is the Mach number.
As the aircraft speed increases, the Mach angle decreases, which means that the aspect ratio should become smaller and smaller. At hypersonic speeds, the delta wing (or a modified one) is the best option as the wing needs to be pretty short for aerodynamics and structural reasons while able to carry the required fuel and generate lift.
The main advantage of the SR-71 Blackbird is its speed, which was about Mach 3.3. It is logical that its replacement should have better speed characteristics. SR 71 used a ramjet during its high speed dash, while its (rumored) successor is expected to use a scramjet engine.

"Turbo ram scramjet comparative diagram" by GreyTrafalgar - Own work. Licensed under CC BY-SA 3.0 via Commons.
The first one(a) is a turbojet engine, the second one(b) is ramjet, and the third one(c), a scramjet. The ramjet and scramjet engines are similar, though the combustion happens at supersonic speeds in the scramjet engine.
NASA has a hypersonic aircraft for experimental purposes called the X43,which uses a scramjet engine, though the aircraft size is pretty small compared to the A340.

Source: hapb-www.larc.nasa.gov
The closest actual aircraft have come to the shape of the 'Aurora' are the experimental aircraft like the X-37, which has short wings.

"Boeing X-37B inside payload fairing before launch" by US Air Force - http://www.af.mil/News/Photos.aspx?igphoto=2000374856 (direct link). Licensed under Public Domain via Commons.
There are a number of aircraft with triangular wings, most notably almost all European combat aircraft have delta wings.
And by the way, the Lockheed Martin SR 72 Aurora concept looks like this.

"Lockheed Martin SR-72 concept" by Source (WP:NFCC#4). Licensed under Fair use of copyrighted material in the context of Lockheed Martin SR-72" href="//en.wikipedia.org/wiki/File:Lockheed_Martin_SR-72_concept.png">Fair use via Wikipedia.

Could you clarify the reference to the image of the turbine/ramjet/scramjet, for example by referencing a,b & c in the text? I guess people who don't know anything about ram/scramjets will not know what's what.

@ROIMaison. I've added the references. However, please do note that this is just a comparative diagram, nothing more.

Strictly speaking, the SR-71 actually used turbojets with compressor bleed and a very effective afterburner. The afterburner acted much like a ramjet, and was almost the only source of thrust at maximum speed. See also http://aviation.stackexchange.com/questions/14710/what-is-a-ramjet.

@NathanTuggy You're right. Basically the afterburner acts like a ramjet combustor. I didn't go into much details because the question was about wing planform rather than engine.

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Could a blown wing ever be powerful enough to lift an aircraft at zero forward velocity?
Theoretically, could an aircraft, using any manner of self generated air flow over the (fixed) wing, ever gain enough lift in order to take off (or just simply lift off the ground) at zero forward velocity?
I am guessing that if an aircraft and its engines were light enough, you might be able to provide a high enough airflow across the wings using the propellers (akin to forward motion) - although obviously I am fully aware that most of the important control surfaces would not be functional. This is just theoretical.
To what end.. well... a more efficient understanding of self-generated lift (possibly?) might result from research into extreme blown flap/wing super-STOL utilization. High-lift, small transport aircraft operating out of small congested city air/heliports with very small runways.
I am aware of the limitations of such designs, such as inefficiency at higher speeds and, in the absence of variable form and geometry (which would add too much weight) the fuel usage would become prohibitive. It's purely an idea for speculation.

Maybe you should set some limits on your question.  Does it have to be manned?  Would bug or bird sized aircraft qualify?  Would rotating wings (helicopter) qualify as "self generated air flow over the wing"?

I don't have the data to provide an answer to the question if a plane can fly by self-generating airflow over the wings. What I can say is, there are cases where light planes have become airborne because of very high wings blowing directly to the plane. Here is a video of a parked plane "taking off": https://www.youtube.com/watch?v=TlEKiSwttsc As you can see the plane doesn't generate the airflow over the wings by it self. It's the high-speed-wind that provides the airflow.

As you can see, the flight didn't last very long ;)

Yes. It's called a helicopter.

You seem to be suggesting some sort of engine blowing air across the wings to generate lift. That doesn't make sense. The wing is much, much less than 100% efficient at converting airflow into lift. You'd get massively more lift just by pointing those engines downwards.

@DavidRicherby That would be a lot more efficient, but not nearly as much fun. :)

@reirab Killjoy -->

Ok. I guess I could have asked / or pitched the question slightly differently. Obviously I was referring to fixed wing. And I guess I also meant an aircraft large enough to be considered a passenger carrying craft, although the actual size is somewhat irrelevant.

@DavidRicherby I also should have made it more clear that, I wasn't suggesting that it would be a good idea. In fact, I know that it would be a really stupid idea in practice. I was merely posing a yes/no question of whether a plane (perhaps tethered, if you like, to prevent the airflow providing forward thrust in our imaginary scenario) could achieve positive lift by blowing a self generated airflow of your own wing.

Yes, and such aircraft are called helicopters. The helicopter rotors work as wings, not as propellers, as they provide lift in the same way fixed-wing aircraft wings do.

@vsz Helicopters are not fixed wing (see the OP's comment right above yours clarifying that he was asking about a blown fixed wing.)

I guess an idea of the power required to self-create lift can be obtained looking at a wind tunnel. The aircraft engine power must be similar to the tunnel engines power (prorata the ratio of the aircraft / tunnel sections ratio).

Just a little physics check here, not meant to be condescending. If the plane self-generated backwards airflow, the reaction to that would push the aircraft forward. In other words, thrust. So you'd get the faster air over the wing, plus faster air from an increasing plane speed too. Best of both worlds. Sounds like what you want is a propeller (maybe with a duct to direct all thrust over the top of the wing).

You may find some extensive research work on this related to https://en.wikipedia.org/wiki/Rockwell_XFV-12

Technically speaking, yes, it's possible, but wildly impractical.
Of course, as usual, Jan Hudec's explanation of the physics is completely correct. Whatever is blowing enough air over the wings to fly would generate an insane amount of forward thrust, meaning that you wouldn't stay at zero forward velocity for long.
However, it's completely possible to apply another force in the opposite direction equal in magnitude to what would otherwise be the net forward force produced by the engine(s) blowing the wings. This would yield a total net forward force of zero, thus no forward acceleration would happen, allowing you to take off at zero forward velocity. Of course, you'd want to make sure that whatever is applying this force isn't also blowing the wings in the opposite direction, otherwise you lose your lift.
Some possibilities for providing this force:

Normal jet engines mounted backwards
Normal propeller engines with negative pitch
Rocket engines mounted backwards
A (really strong) tether
Wheel brakes (this only works as long as you're on the ground, of course... you'd start accelerating forwards very quickly as the wheels break free from the ground, but you could technically leave the ground with zero forward velocity.)
A really big machine gun, such as the GAU-8 Avenger or Gryazev-Shipunov GSh-6-30
Lots of AK-47s ('lots' being a number roughly equal to the net forward thrust of the engines in pounds divided by 13)

This is roughly what the backwards-mounted rockets would look like:

C-130 Rocket Assisted Landing
Source: YouTube
Another possibility to technically meet your requirement of taking off at zero forward velocity would be to simply start off rolling backwards fast enough that you would accelerate forwards to zero forward velocity at the moment the tires leave the pavement. :)
Of course, as you've hopefully figured out by now, that all of the above are wildly inefficient ways to take off. They would, however, technically work. And, of course, in the case of the GAU-8, whatever is in front of you during the takeoff is going to have a very bad day.

@jjack That paragraph was a joke. What I described in that paragraph would still have zero horizontal velocity at liftoff. It would just be non-zero prior to liftoff, thus still technically meeting the OP's requirement (as he didn't say it couldn't have a non-zero horizontal velocity before takeoff.)

I assume simply canting the wings far enough back that much of the lift generated acts to counter the thrust forward has been discarded as a possibility for good and sufficient reasons?

@NathanTuggy Any AoA that doesn't result in the wing being stalled will still leave a rather large forward force. I was assuming from the way the OP asked the question that he wanted the wing to be generating lift in the normal way (i.e. not stalled.) Blowing the wings just below the critical AoA would be certainly be helpful, but it wouldn't completely eliminate (or even come close to completely eliminating) the forward force.

@reirab: Fair enough, although I would like to see any detailed calculations/diagrams you can dig up.

Those speed-braking C-130s were for the purpose of landing in a soccer stadium. Right next to the American embassy.  In Tehran, Iran.

What you're asking for is basically a helicopter: rather than blowing air over the wing it's more efficient to attach airfoils to a vertical axle and generate relative movement (and hence lift) by rotating them.

I would say, your answer should be: "Yes it's definitely possible - It's called a helicopter" :) Seems to be the best answer IMHO. +1

I know all of the above, it was merely a speculative poser. It's an absurd question, but I guess I was just wondering whether enough of a pressure differential could be created using self generated airflow over a fixed wing, perhaps tethered to prevent forward motion.

No, it would not.
To take off vertically you need to apply vertical force equal to the weight of the aircraft and no or just a little horizontal force to possibly start moving.
Now the total force on an aircraft (any aircraft) has opposite direction to (average) change of velocity of the air flowing around the aircraft, and magnitude proportional to magnitude of the velocity change and amount of the air.
So to lift off, the aircraft has to accelerate air down a lot. In normal rolling take-off, the air is moving horizontally around the aircraft, so the wings need to only bend it down a little to generate sufficient downward acceleration and corresponding lift force. But in vertical take-off the air is not moving, so it simply needs to be accelerated downward.
But a wing is not capable of bending the flow by 90°, only maybe 30° or something like that, so to give the air enough vertical velocity you'd also give it even more horizontal velocity, generating a lot of thrust.
For all that thrust you would need to provide energy with the engines. It means thrust/weight ratio at least 2:1. No aircraft has that. Conventional aircraft can do with 0.2, VTOLs (including helicopters) need 1 and a bit. 2 is absurdly inefficient. And it would not be true vertical take-off as the aircraft would accelerate horizontally very fast.
With circular shape Coandă effect can bend the air by more, but that does not really count as wing any more. And it still does not have any advantage over rotating the thrust vector itself. The advantage of blowing engine exhaust over the wing is not that it would be more efficient, it is that it is simpler than rotating the engines.

The last point is the important one - rotating the thrust vector itself is far easier. So I would agree if the question was if it was reasonable to do that. But concerning the possibility, I have three concerns: a) Why would an aerodynamic surface with a 70°-80° deflection angle not be called a wing? b) There are turbofans with a thrust/weight ratio of around 6, so a system thrust/weight of around 2 is not unthinkable (it would look very silly, admittedly). c) You could canel out the horizontal thrust with two counteracting engines (again, silly, but possible).

@JulianHzg See my answer below. :)

@jjack: You have to remember that all physical laws hold at the same time. Newton's third law requires that if the air applies upward force on the aircraft, the aircraft must be applying downward force to the air and the Newton's second law requires that the air is accelerated downward proportional to the force acting on it since it is free to do so. The forces are created by the pressure differences, but that is totally irrelevant to where the air ends up moving. Newton's laws require it to be down, so down it is.

Jan, whilst I know that some lift will always be generated via 3rd law momentum reaction, I personally subscribe fully to the pressure difference model of lift. Why? Well, because I am aware of many stol aircraft that can get airborn at 10 knots, with a total downward reaction air weight of just a few kilograms in relation ot the weight of the plane. The enormous lift (as demonstrated by controlled lab measurements using barometric instruments placed above and below the wing) far exceeds any lift generated by 3rd law reaction. I have no clue why it's still disputed.

@RussBoys, it is still disputed because it is a total misconception that still does not want to die. There is no some lift generated by 3rd law reaction and other lift created by something else. There is just aerodynamic lift and a bunch of physical laws that apply to it and one of those laws is 3rd law: all force the air applies to the aircraft must have reaction force of the same magnitude and opposite direction that the aircraft applies to the air. And since the air does not have any solid support, it accelerates according to the second law.

@RussBoys, the second law does not require the mass of the reaction air to be comparable to the mass of the aircraft, it just requires that force equals mass time acceleration. The air is accelerated a lot. And it also is quite a lot of air: all air within the wing span and to comparable height. both below and above the wing. Yes, the air above the wing is also reaction mass and it is also accelerated downwards. It is also applying force (more than the air below the wing, in fact) and the laws of motion apply to it, so it is accelerated.

Jan is right. Whether you look at the lift as a pressure difference or as the equal and opposite reaction of the force applied to the air (both above and below the wing,) you get the same numbers. Both are just different ways to describe the same thing. There are tons of questions on this SE about how this works.

Maybe.
You would need a very special kind of wing, one which controls the flow direction at the trailing edge by blowing. Such a concept had been tested by AeroVironment in the 1980s and in a model, but to my knowledge no man-carrying airplane using this concept exists.
The cross section of the wing's airfoil is a circle, with an exhaust slot at the back. The exhaust stream of a gas turbine is channeled through the tubular spar of the wing and exits through a spanwise slot in a collar around the spar. By rotating the position of the slot and pumping enough air through it, you can control the amount of circulation this wing creates.

The exhaust position of the inboard wing can be used to control lift, like flaps do on a "normal" wing, and the outer part takes over the function of ailerons. By pointing the exhaust straight down and with a sufficient air mass flow, this wing can indeed take off vertically. Efficiency will be nothing to write home about, however.
A blown flap in the conventional sense needs external flow, because its own mass flow is far too small to create sufficient lift. All it does is to invigorate an old, spent boundary layer, so it will stay attached over the contour downstream of the blowing point. Without speed, no external flow exists which could be influenced, except for a small quantity dragged along by the airstream of the blown flap.
A similar, albeit less radical, idea was used in the British research airplane Hunting 126. It used the exhaust gasses from its fuselage-mounted Orpheus engine to blow air over its flaps. Additionally, it had small nozzles at the end of the fuselage and the wing tips for low-speed control, just like the Harrier Jump Jet. However, it needed some forward speed to create enough lift to fly.

Hunting 126 in flight (picture source).

Using the Coandă effect, it is theoretically possible for an aircraft's engines to blow enough air over the wing to generate lift.
However, in a real aircraft the engines are placed so as not to place the complete wing within their outflow. Otherwise, a large amount of drag would be constantly produced during forward flight. Engine outflow also does not have sufficient cross-section to affect the complete wing, unless a very stubby (small aspect ratio, not very efficient) wing was used.
Applications have been seen in prototypes such as the Boeing YC-14 or production models such as the Antonov An-72, however these were STOL aircraft, not VTOL.

Interesting. Thank you. I didn't consider that. But useful to know for further research.

I'd say vertical takeoff in a non-rotating wing, not deflected thrust machine was obtained in the Custer Channel Wing models, you have some videos in YouTube https://youtu.be/-Sn5JL9t_C4 http://www.flightglobal.com/pdfarchive/view/1952/1952%20-%200044.html http://www.angelfire.com/va3/bythefire/
NASA Technical Report Server -NTRS- has a L53A09 full size wind tunnel report of this arrangement http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930087470.pdf
   and links to the Custer follower's sites exist in Wikipedia

A partial "Yes" can be seen if you look at the AvroCar:
https://en.wikipedia.org/wiki/Avro_Canada_VZ-9_Avrocar
This was never even close to be commercially useful, but it DID fly.
The reason I said 'partial' above, is that some of the lift comes directly from the engine pointing downwards, if I understand correctly, but the whole point of this craft was to investigate the coanda effect.

JulianHzg asked if a surface with a large (70-80 degree) deflection angle could be called a wing.  The Harrier has such a surface.  If we are willing to call the exhaust nozzles "wings" then we have a working example.

Exhaust nozzles aren't wings (or airfoils at all,) though. A helicopter is closer to what OP is asking for, since it actually does cause wind to flow over airfoils (the rotor blades) even when it's not moving horizontally, but OP was asking about a blown fixed wing.


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Is there any way to stop a pilot from crashing an airliner?
If a pilot decides to crash an airliner, a la Germanwings or Egyptair, could he be stopped?
In those cases the offending pilot waited until he was alone in the cockpit to act. Thus many airlines have made it mandatory for there to be two crew members in the cockpit at all times, even if it's just a flight attendant to stand in there and wait for a pilot to return.
Although that might give passengers some piece of mind I am doubting that it would do much good. It seems to me that, even if the other pilot is in his seat and strapped in, if a pilot decides to crash the plane he could kill the engines and put the plane in an unrecoverable attitude very quickly.
Is this a correct assumption? Would Airbus envelope protections prevent this? Can the plane be placed in direct mode to override the protections?  What about a 777? Does the yoke feedback system allow one pilot to overpower the other?  The engines could easily be throttled back, but could they be quickly shut down requiring a restart? What could the other pilot do to stop his actions?

I'm mostly asking what the other pilot could do and if FBW aircraft make the scenario more difficult. If it seems too much of an opinion question focus on the specifics mentioned in the last paragraph. Can engines be killed and could a plane be put in an unrecoverable attitude quickly

As it's currently worded, this seems like a whole lot of questions rather than a single question. Maybe it would be better to focus on a single scenario? Whether there's a way to stop a pilot from crashing an airliner seems like it will be very specific to the particular scenario. It's also worth noting that shutting down the engines of an airliner is far from ensuring a crash. From cruise altitude, most airliners can glide around 100 miles with no engine power.

@reirab Yeah, but dead engines would make unusual attitude recovery more difficult. And engines need some fairly specific speed and altitude parameters for restart. Maybe I can break it down. I'll have to do it later, though. Asked the question during lunch. Unless you feel like fixing it

It might make it harder depending on what the unusual attitude in question is. For others, it might not matter at all. And some attitudes might even be made worse by having the engines produce thrust (e.g. a steep dive.) Once you have time, this seems like it would be a better question if it described a particular set of actions of the suicidal pilot and asked if/how those could be countered. Setting up a particular "threat model" of what you're trying to counter is usually the first step to determining an effective counter in the security industry.

COULD you do that?  Sure.  The relevant question, though, is if the tradeoffs involved would be worth it.
How could you do that?  Essentially, a trusted 3rd party could have the ability to disable all controls that the demented pilot has access to and assume all control over the aircraft.  If you're willing for somebody in the network operations center to have the ability to "turn off" every switch & control in the cockpit and remotely pilot the airliner to its landing, then you're set.  The pilot is now every bit as much a passenger in the aircraft as everyone sitting behind him is, and short of taking the crash ax and causing a depressurization, he can't affect things that much.  (And even if he did that, the airplane still won't crash.)
The problem with that plan is obviously that if the remote control function gets taken over by hackers or a demented individual at the operations center, the pilots are helpless to intervene.  After all, for the demented PILOT to be rendered harmless, you have to remove ALL ability to override the remote control, all ability to pull circuit breakers, all ability to affect everything.
So, where is the greatest threat?  A demented pilot that overcomes the other pilot (by force, by locking him out of the cockpit, whatever), or problems at the operations center or in the remote control process?  The track record of airline pilots is unmatched by nearly anything else for reliability and resilience, and we aren't nearly as vulnerable to being hacked as any remote control datalink would be!
The general understanding is that the best solution is to keep the pilots in control of the aircraft, and have measures in place so that if one of them loses it, the other pilot can keep things going.  Things like having a flight attendant in the cockpit to let the other pilot back in (would have changed the course of the Germanwings flight) can go a long way.  Or if there is a struggle for control, a pilot could summon the flight attendants over the PA to get help restraining the madman.
Perfect solutions? No.  But better than allowing the aircraft to be taken over by somebody outside!
After all, while "pilot goes nuts" is a vivid headline, the extent of the actual risk is quite limited.  Millions & millions of commercial flights happen without incident every year, and introducing a slew of new risks in the form of remote control that can't be over-ridden, seems like a severe over-reaction to what is in fact an incredibly remote scenario.  There are better ways to deal with the extremely rare & unlikely "crazy pilot" possibility than that.

We've had a question or two about the remote control thing. Clearly that is exactly the wrong thing to do. Even without the spectre of hacking you would then have to trust, not only the pilots, but the persons on the ground that could do an override. And their life would not be at risk. Bad bad bad!

And still, the guy on the ground would have no more ability to recover from dead engines and an unrecoverable attitude than the other pilot would.


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Why turn off pitot tube heating?
I'm merely an amateur simulator (X-Plane) pilot. On a flight yesterday the airspeed indicator stopped working. After the initial panic I remembered reading something about pitot tubes freezing, found the pitot heating switch, and turned it on. The problem was resolved immediately.
This led me to think: Is there a good reason to not turn pitot heating on before take-off, and leave it on for the entire flight?
I'm flying a Sud Aviation SE 210 Caravelle

a defect in flight which forces you to turn it off

to add to @ratchetfreak's comment, you don't want your pitot heat on with a failed generator/alternator for example (unless you really have to), as it'll drain your battery rather quickly.

@falstro Unless you are in icing conditions in which case you have bigger problems if you turn it off.  A better example would be an electrical short in the pitot heat system.

@Lnafziger that's the "(unless you really have to)" part. An electrical short in the pitot heat system would probably trip a separate breaker, so turning it off doesn't actually do anything in that case (if the breaker would have covered multiple systems you could turn it off and reset the breaker though).

@falstro: Isn't "no working generators" a land-immediately-even-if-you-have-to-do-it-in-a-field situation (thus rendering the pitot heat's power consumption irrelevant, since you aren't going to be continuing the flight anyway)?

@Sean airplanes fly just fine without generators. And they have quite capable batteries too, yes you'll want to land as soon as practical, but depending on the situation it's probably safer to land at an airport. Safer still if you have a functioning radio, which can run on battery for quite some time - provided you turn off non-essential, battery-draining, equipment :)

The aircraft checklist will determine when the pitot heat should be on. Strictly speaking, if the checklist says it should be on, the only reason it should not be on is if the system is inoperative or is causing some issue (if the generator system fails it will drain the battery, as falstro commented). The checklist linked by Lnafziger has the pitot heat ON before takeoff and OFF after landing. Other times it may be "as required" by conditions.
The pitot heat makes sure the pitot system remains free of ice. Failed airspeed, especially in IFR conditions, can be serious. The failure may not be obvious, leaving you to stall/overspeed. Leaving the heat on can cause the system to overheat. While some systems automatically protect against this, not all will (especially with smaller aircraft).
Checklists for larger jets also seem to have probe heat on before taxi and off right before shutdown. The reason for this is probably safety. Modern aircraft rely heavily on pitot static systems. AF447 crashed partially due to icing on the pitot tubes. Why leave it off and run the risk of icing? The cost of leaving it on is fairly low.
On smaller aircraft where the pilot may even be able to see the pitot tubes, the situation may be different. These aircraft have less automation, and the cost of repairing a pitot heat system is higher relative to the rest of the aircraft's maintenance. However, the issue of safety remains.

Actually, very few light GA aircraft should be operated with pitot heat on all the time. Unless it's in the checklist, it should be turned on before (or, at the least, upon) encountering visible moisture. I've not seen any checklists for Cessna, Piper, or other light singles that suggest the pitot heat should be on during normal VMC operations.

@egid: I'm curious, why not?  (Given that "no airspeed information" basically means "imminent life-insurance payout"...)

Because the heating element runs very hot and will eventually burn itself out, and replacing it (like any other aviation part) is expensive.

I'm not sure what kind of airplane that you are flying in the simulator, but the checklists for jets typically do have you turn the pitot heat on just before takeoff and leave it on until after landing, just so that this is less likely to happen.

Update: I found a French checklist for the Caravelle and it says to turn on the pitot heat before takeoff:

Rechauffage Pitot.....MARCHE

OK, that makes sense. I'm flying a Caravelle, will look into its checklist.

Piston aircraft checklists usually have "pitot heat on" before takeoff and "pitot heat off" after takeoff,. But that doesn't mean it is expected to leave it on all the time. Other checklists (such as "flight into icing conditions") have "pitot heat on". Is pitot heat expected to be on all the time with jets?

@DJClayworth Yes, and that's why they are written that way, even in the piston airplanes.  They put it in the icing checklist just in case it was forgotten previously.

Jets that fly up into the flight levels are always flying in conditions well below freezing.  It makes sense for them to have Pitot Heat on for the duration.

@SkipMiller Usually, but they are also usually above the weather and not in icing conditions for the vast majority of their flying time.  It's simply a precaution and most manufacturers would rather have the pitots on and not need it than the other way around.

for what is worth, Diamond checklists (after initial pitot heat test on/off) say "PITOT HEATING  ... AS REQD."  before-takeoff and "OFF" after-landing

@Radu094 .. and the Socata checklists don't mention it at all. :) (except preflight and icing checklists)

@Radu094 That's why I said jets in my answer.  :)

At our airclub, the checklist for C172 shows:

... stuff ...
Pitot heat on, check tube warm, turn off.
... complete the walk-around... start... taxi to engine run-up... do run-up...
Do final pre-take-off checks, one of the last of which is "pitot heat: ON".

I've seen some C172 checklists that say "as required" instead of "on" near the end.
There are no further pitot heat items on the checklist except for the "after landing checklist". So we're supposed to just leave it on.
During my initial training my instructor mentioned that we turn it off until just before take-off because it can overheat and fail if operated while stationary. I don't remember seeing this in the C172 operating handbook, so maybe they're just being overly cautious or something.

In my experience, the procedures you describe are not typical SOP for the C172, but are in line with what you would do in the larger aircraft that many pilots are working towards flying in a career.

Although pitot heat is quite reliable, it can burn out much like an incandescent light bulb.  Why waste its useful life without immediate reason?

Because the price of needing it and not having it on can be quite high. The same could be said for reserve fuel.  Why do we carry it around all of the time if we don't need it?  It's there for those times that we do (and you might not even know that the pitot heat saved the day if it were already on).  Personally, I just follow the manufacturers recommendation. If they say that it should be on during flight, I turn it on for the entire flight and don't second guess them in order to possibly save a few dollars.

If the pitot tube is giving a partial reading that is 95% accurate...  You may need it on and not even really know it.

You can buy spare pitot tubes.  You can't buy spare lives.

On the ground, without airflow over the pitot tube to cool it, it will burn out very quickly. By operating something like this when it's not needed you risk not having it available when you need it.

While this may be true for some aircraft, others automatically prevent it from overheating. If the checklist tells you it should be on, then it's probably fine to turn it on.

To clarify, the aircraft I'm familiar with, large part 121 transports, do not have any means to prevent overheating of the pitot tube. Newer aircraft do have means to prevent the heaters from coming on while on the ground if at least one engine isn't running and also lower power while on the ground than in the air. Old birds (e.g. 737-200) just put the heat on when the switch is on.


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Did commercial airliners have microwave ovens in the past?
So I went on 2 long (total of 16 hours) flights with a major US airline, and they did not provide a free in-flight lunch (grr) during either flight. I had brought a sandwich with me just in case, but when I asked the flight attendant if they could heat it up they said that they did not have microwaves. This was I think a 757 or similar aircraft.
When I landed I was asked about my trip, the microwave thing came up and was told (by an older person) that airlines did have microwaves and that mothers with children would often ask the flight attendants to warm up bottles of milk for them...?!
So now I'm curious, did aircraft used to have microwaves in the past? Were they removed? I now know the food they serve on airplanes is "heated via hot air ovens" but why would there not be a microwave on board? Even if just for crew use?

The food is usually not heated at the airport, but aircrafts  have hot air ovens. I guess this is the reason why the food is in aluminum bowls. Plastic usually is a bad idea in such an oven, and also your sandwich should have been placed in a aluminum bowl, if they heat it for you.

I stand corrected then... Didn't know that!

They might have warmed the milk by putting the bottle into a pot/carafe of hot water from the coffee maker.

Generally speaking, airliners do not have microwave ovens for safety reasons. I could not find any reference where commercial airplanes used to have microwaves. Probably some smaller business jets have them.
Some flight attendants mention that they can warm your food, but some say that they will not for legal and health reason.
As also mentioned by sweber in comments to the question, meals are not heated at the airport. Airline catering companies like LSG Sky Chefs prepare the meal near the airport and deliver it to the airplane. Inside the airplane, they use convection ovens to heat it.

I'm not sure about airliners (7x7, A3xx, MD-80/88/90, etc.), but you can definitely get microwaves on some business jets

Could you expand on "safety reasons"?

haha, yeah, they'd have to heat your supper really hot if they heated it on the ground, since it's usually not served until 1-2 hours after takeoff... and that's to say nothing of what they'd have to do for the breakfast served 12 hours later.

@reirab So it's not that microwave oven could burn something down or alien rays problem?

I flew for TWA International from 1970-1990. We had microwave ovens on all of our 747's. It took a long time to train the older F/A's on their operation. Prior to their installation we cooked in convection ovens which cooked meals for 30-40 minutes depending on if they were frozen. Now you're telling me I can do this in 3-5 minutes? We destroyed so many Filet mignons by turning them into hockey pucks. Plus we had to warn the passengers with heart monitors that microwaves were onboard and in use. It was quite a learning curve.

For the most part, no, they did not have microwaves onboard passenger aircraft. When serving large numbers of passengers a microwave would be a luxury taking up valuable space. Having said that I did work for an airline that did have microwaves onboard.  It was an all first class airline with a small fleet of
B727's.  The aircraft were configured for 33 passengers. There were no menu items that were ever designed with the microwave in mind as a preparation method. Some chefs would use it to reheat a plate of food in a crunch but it was against policy and it would create fireworks onboard as the English bone china had a gold emboss on it that would spark. Hot water would be the only way a baby's bottle could be heated. Even if they had the ability to heat your sandwich they are correct in not allowing that due to health, food and safety regulations. Above all else, most passengers with manners would agree, it's a rather tacky request.

Some formatting would make your answers much more readable.

Expanding on food safety reasons,  When you go to a restaurant and are served food, the restaurant knows who served you the food, who made you the food, who prepped the ingredients and finally they know the companies the ingredients came from.  All are monitored by management following guidelines and inspections set forth by the health department. You bring in your own sandwich and want us to warm it up. we have no history on this sandwich, it could have been in your gym locker for all we know.

please feel free to edit that in to your answer text instead of adding it as a comment.

"A rather tacky request?" It may not be a request the cabin crew can fulfill, due to lack of equipment and/or company policy (the crew could spend the whole flight heating people's meals if this was a service they offered), but tacky? It's really not an unreasonable request at all, but unfortunately, it's not a service airlines usually provide.

It strikes me as tacky, too!  :)

AA has Microwave Ovens on its 777-300 First Class Galley.

Welcome to Av.SE.  It's helpful if answers here have a little more weight than "a post on the internet says ___".  Are you an AA Flight Attendant who works on the 777-300's?  That sort of background would add credibility to make this a better answer. (And if you aren't AA but have, maybe, non-revved on them, that's cool too... you still know your way around a galley better than the rest of us, and if you've seen them on there recently, that's a good data point.)


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Can I use a LAPL/PPL issued by the UK CAA to fly outside Europe?
Will the Light Aircraft Pilot License (LAPL) or Private Pilot License (PPL) be enough to to be able to fly to other countries outside Europe?

PPL(A) or LAPL(A)? Your text is a bit ambigous there...

Well, which one is better?  Is the PPL better than LAPL?

The EASA issued LAPL(A) is limited to 2to MTOM, 3 passengers max and only valid in European countries. A PPL(A) issued by an EASA country does not have these restrictions, but can be subject to local restrictions in the non-European country you want to flyin, e.g. you cannot use the EASA PPL(A) to fly in the US without further paperwork.
For more information, see the UK CAA's page on the LAPL.

Your LAPL(A) is a lifetime licence that contains SEP(land) and/or TMG privileges restricted to non-complex EASA aeroplanes with a maximum take off mass of 2 metric tonnes and a maximum of four people on board.
You can fly more complex aeroplanes within the privileges if you have 'differences training' signed off in your log book by a suitable instructor. The LAPL is also valid on non-EASA UK registered aircraft in the UK.
The LAPL requires an in-date EASA Part-Med Medical Certificate, at LAPL level, but Class One or Class Two certificates can also be used. A valid JAA Class One or Two medical certificate is also acceptable. But you cannot use your LAPL with an NPPL medical declaration.
The SEP(land) or TMG endorsement on this type of licence is not issued as a rating. So there is no rating expiry date. Instead you must follow self-validity checks on your own flying history for the past 2 years to ensure currency on the day of your planned flight.

Further Reading from the UK CAA:
EASA Light Aircraft Pilot License Aeroplane - LAPL(A)
EASA Private Pilots Licence Aeroplane - PPL(A)


text:
Will the frequency 122.000 MHz no longer be used for Flight Watch after October 1st 2015?
The Flight Service Program Changes announcement from the FAA includes

On October 1, 2015, the FAA will consolidate Flight Watch services into routine flight services inflight frequencies to eliminate unnecessary duplication of service and provide greater convenience for pilots. These services provide inflight weather information to pilots. After that date, these services will be available on the same frequencies that pilots use to open and close flight plans and to receive updates on NOTAMs or Temporary Flight Restrictions (TFRs). Dedicated Flight Watch frequencies will be decommissioned.

What are the “dedicated Flight Watch frequencies,” plural? The mnemonic drilled into my head was Flight Watch on 122.0, with the zero shaped like the face of a wrist watch.
The only frequencies I, a student pilot, have ever used for opening and closing flight plans has been RCO. The wording above is not specific, so does that mean instead of one dedicated frequency, you have to know the local RCO frequency to call Flight Watch?

Below 18,000 feet MSL, En Route Flight Advisory Service (EFAS) (a.k.a. Flight Watch) is provided on 122.0 MHz. Above this altitude, it is provided on discrete frequencies, with each one serving a specific ARTCC area (see AIM 7-1-5, FAA JO 7210.3Y Section 3).  These discrete frequencies are listed in the margin of IFR Enroute High Altitude charts:

To answer your original question, the FAA plans to consolidate EFAS onto existing Flight Service Station (FSS) frequencies on October 1, 2015. Because Lockheed Martin (the FSS contractor) has consolidated flight service stations, the EFAS weather briefers are now co-located with Flight Service personnel (they physically sit next to each other in the same room), making it possible to obtain both services on the same frequency.
At the same time, the FAA will phase out legacy Remote Airport Advisory Services and more significantly, require the ICAO format for all flight plans (international AND DOMESTIC), see Flight Service Program change announcement.


text:
How to get the correct angle when doing a visual appoach before landing?
Before landing, without ILS, how can you get the correct vertical angle and know when you're too high or too low?
I think there are some red and white directionnal lights next to the runway that can tell you if your angle is correct, but I'd like to know precisely how a nice approach is done.
Do pilots sometime just figure it out because it's a habit? Is it more difficult if the runway is surrounded by an ocean?
I'm talking about commercial airliners as it seems more simple with small aircrafts.

depth perception, the runway edges side to side are parallel so you can use that to see where you are height wise

I would add, in addition to my answer, that you must be familiar with an unlighted runway, by studying the maps and making several circuits, if needed, before attempting to land. Some runways have obstacles near the runway ends (trees, antenna's, houses, etc.). A small field my father uses is quite well obstructed.

PAPI
An airport might have Precision Approach Path Indicator (PAPI) lights set up. I believe these might be what you are thinking of. They are discussed in Chapter 2 of the AIM.
Here are two pictures to show them at night.

The first, shows a plane that is on the correct glide path. Firstly, they are normally installed to the left of the runway, and according to the AIM, red should be on the right, so, I believe the picture has been flipped, however you could still use them as is.
If you are right on the correct glide scope for that runway, you would see two white and two red. .2 degrees high would show three white and one red, and .5 degrees high, or higher, four white.
Conversly, .2 degrees low will show three red and one white, and .5 degrees low or lower will show all four red.
Red and White is Just Right. All Red, You're Dead.

VASI
There might also be VASI, or Visual Approach Slope Indicator, lights. These are in many different configurations. They are also discussed in the AIM at the same link I posted above. An example of a two bar VASI light setup is shown below.

The VASI lights are the two sets of two lights next to the runway (just above the row of green lights. They are set up so that white over white is too high, red and white both showing, on glidepath, and red over red is too low.
The mnemonic for those is: red over white, alright; red over red, you're dead.
For more information, there is the AIM Page, the PAPI Wikipedia Page, the VASI Wiki Page, plus there are many other pages which are useful. If you search (using Google or BING, for example) for "runway lights papi" or "runway lights vasi" you'll get many hits.

One last comment here. The correct glide path for an airport is not always the same. If there is/are an obstacle, the glide path might be higher/steeper. If the runway is lighted, using PAPI and/or VASI lights, use them! They will keep you on the correct glidepath for whatever runway you're trying to use.
Good Luck and Safe Flying!

All true, but sometimes there is no PAPI or VASI and the pilot is still able to land.  :-)

That's exactly what I was thinking about, but I don't understand the difference between the PAPI and VASI, though they are disposed in a different manner. And how can you lan without those lights in a big plane?

I'm sorry, in the body of the question, the OP mentions lights, so my assumption was he wanted information about runway lighting. My bad.

A 'big plane' would not normally land at an unlighted runway. In an emergency, if you have the altitude of the runway, along with obstacles either visually identified or hopefully off of a chart, you can calculate the landing. Is that what you want to know? How to calculate things like when to start descent, from what altitude and distance?

@CGCampbell There are many runways, even at larger airports, that don't have vertical visual guidance. They often do land on unlight runways (during the day) and there are times that the PAPI/VASI is broken, and they don't close the runway because of it. I read his question as asking both about the lights (which you have done a great job of answering) and what to do when you don't have them (how do you get the correct angle without them). I'd add one more part to your answer describing the use of instrument approaches as a backup and a visual only approach to completely answer the question! :)

Well, I've tried writing a new answer three different times, all based on the FAA's Airplane Flying Handbook, and I've tried to incorporate the part discussing what and where to focus your vision externally, including the blurring due to speed. Also tried to add in the angle of the runway edges to help determine altitude, with the three pictures of how the runway should look. Unfortunately, every time it simply becomes a quote, or too darned long. I can't seem to get it in layman's terms. Perhaps one of the others here can do a better job. Sorry.


text:
Do crews look for "Dr." on a passenger manifest to identify medical doctors?
With many airlines, when a passenger buys a ticket online, there is a space for them to select a "title", such as Ms., Mr., Dr., Rev., etc.    In most social circumstances, the title "Dr." is applicable to anyone with a doctoral degree (M.D., Ph.D., D.D., etc).
I have heard a rumor that in the event of a medical emergency on the plane, the cabin crew will check the passenger manifest for people who have given the title Dr., in hopes of finding a medical doctor who can assist.
As a consequence, goes the rumor, a passenger who has a doctoral degree, but is not a medical doctor (say, a PhD in mathematics), should not choose the title "Dr." when buying a ticket, since if there is a medical emergency, the cabin crew might waste time asking this mathematician for assistance.
I have also heard it said that this is nonsense, that crews would not bother looking at the manifest, and would simply make a PA announcement asking for anyone with medical training.  (This has the advantage that it would also identify medical professionals such as nurses, paramedics, etc., who would not use the title "Dr." anyway.)
Which of these reflects actual crew training or standard procedures?
What is the best practice for a passenger who holds a non-medical doctorate?  I've never seen any official guidance from an airline on when to use the title "Dr" on a ticket.
(I wasn't sure if this question would be best here, or on Travel.SE, or maybe even Skeptics.SE, but I thought this site would be most likely to have people with first-hand knowledge from the crew side.  I'm open to suggestions for migration.)

When someone shouts "is there a doctor in the room?" They often mean anyone with medical training even if they don't have a doctorate.

I think you'd be better off asking on travel.SE, because it's about commercial air travel from a consumer's point of view.

I do have a PhD, and I select "Dr" if there is a field for that when booking flights. However, it never appeared on my tickets. I don't know if it's on the passenger list.

@casey: Yes, I said "cabin crew" instead of "flight crew".  I assumed the flight attendants would take the lead in finding a medical professional among the passengers, in any case.

You are correct that it is done by PA rather than by reference to the manifest, at least at my carrier in my type of aircraft. As you surmise, the "Dr" notation has too many opportunities for both false positive AND false negative results to be where you want to start when time is of the essence.
Besides, if you need medical help at 40,000', you're probably much better off in the hands of a good E.R. nurse or paramedic than with a radiologist who hasn't done hands-on emergency care since his residency.
Most airlines use a service that's reachd by a phone patch to an E.R. doctor who specializes in evaluating these sorts of situations (and recommending, divert now or continue on), so any medical professional on the aircraft is working under his direction. He is also familiar with the contents of a medical kit carried on the aircraft just for these situations, so he can say "have the (nurse/paramedic/doctor/etc) administer ___ out of the medical kit" already knowing what is & isn't available.
Interestingly, a veterinarian can also administer the same medications the other medical professionals can in this sort of situation!

That's indeed interesting. Although, if you think about it: a vein is a vein, a syringe is a syringe, and a vet will definitely have more hands-on experience than an average physician. Since he is under the direction of a (probably carrier-employed) properly insured doctor at the other end of the phone, the risks, both medical and legal are likely quite low.

especially false positives, and Dr. doesn't mean medical doctor, but anyone with a doctorate level degree.

I understand that a vet has a longer training period than a doctor.when you think of how many different types of animals they have to deal with,but a doctor has only one!

@keithjackson,  In the UK a doctor does at much training after qualifying then they do before, and is only allowed to work on their own once some of the additional training has been done.    So it is hard to compere length of training of a doctor to a vat.


text:
What does "1%" mean in ICAO Annex 14 § 3.9.9 (longitudinal slope changes)?

— 1 per cent per 30 m (minimum radius of curvature of 3 000 m) where the code letter is C, D, E or F; and
  — 1 per cent per 25 m (minimum radius of curvature of 2 500 m) where the code letter is A or B.

Can someone explain what "1% per 30 m" means?
Does it mean 0.3 m of elevation difference for every 30 meters? Or 1/100 per 30 m?

Percent means a hundredth

Thanks hougaard for your response!!!

Assume if my slope is 0.75m in 50m ,will this criteria fits to 1% per 30m?? really appreciate if you can share your calculations for this?

@SaimaHasan if your slope is 0.75m in 50 meters, that will be 0.75/50=0.015, which is 1.5%

You are referring to ICAO  Annex 14 Volume I, Aerodrome Design and Operations. Section 3.9.9 says:

Recommendation.— Where slope changes on a taxiway cannot be avoided, the transition from one slope to another
  slope should be accomplished by a curved surface with a rate of change not exceeding:

1 per cent per 30 m (minimum radius of curvature of 3 000 m) where the code letter is C, D, E or F; and
1 per cent per 25 m (minimum radius of curvature of 2 500 m) where the code letter is A or B.

To better understand this, lets see what the previous section says:

3.9.8 Longitudinal slopes
Recommendation.— The longitudinal slope of a taxiway should not exceed:

1.5 per cent where the code letter is C, D, E or F; and
3 per cent where the code letter is A or B.

So: for a taxiway with a code letter D for example, a maximum slope of 1,5% is recommended. That would be 1,5 meters up or down within a distance of 100 meters.
If a part of the taxiway in question is 1,5% uphill, and another part is 1,5% downhill, the transition from the uphill portion to the downhill part should not happen at a rate faster than 1% within a distance of 30 meters.
In addition to this, the radius of the curvature should not be less than 3000 meters. This means transitions must be smooth within that 30 meters distance.

The important word is "change" - that is, how much the slope is allowed to change - so no sudden sharp edges are allowed, but all connecting slopes (or flats) need to be rounded off by 3000 or 2500m. How much the allowed slope is - will be discussed elsewhere.


text:
How do individually controlled feather like winglets work?
I want to know how the individually controlled feather like winglets work on controlling and rolling by reducing drag.(concept of airbus bird's of prey)
I just need a detailed review of the aerodynamics and its mechanics and how it reduce drag and what are its effect on L/D ratio etc as i am a aeronautical student i wish to know more about it on the futuristic design so it can be helpful in my projects

I think the Airbus is doing research on this to answer the question of how much drag it reduces and how the effect on lift/drag ratio is. So probably nobody yet knows the answer to that.

"I just need a detailed review of the aerodynamics and its mechanics" wow!  :)

Please ask Airbus Marketing. Engineering will not be helpful in this – they still shake their heads about this concept.

The "Bird of Prey" is nothing more than an artist's conception at this point so there is nothing to review from a mechanical design standpoint.
Somebody thought it would be neat to make a plane that looked like a bird, but the methods by which birds achieve flight is far different than in modern aircraft.  I don't believe there are any practical advantages to having a control surface that looks like a feather, and "function follows form" isn't a design strategy that has been proven to work.
I doubt we will ever see one fly, but it would make a fanciful sculpture, like this:


text:
Difference in location of the exhaust nozzle between F-35 and Saab Gripen
The F-35 exhaust nozzle is located a little inside the empennage but in Saab Gripen it is located a little extended from the empennage
What is the reason?
Will this different location of the exhaust nozzle influence the rate of turn?

What you are referring to is not actually the afterburner, it is the jet exhaust nozzle. The afterburner is a system inside the exhaust duct of the engine.

The F-35 exhaust nozzle is located a little inside the empennage but in Saab Gripen it is located a little extended from the empennage. What is the reason?

It's because you are comparing two very different kinds of empennage.

Regarding the vertical stabiliser: The F-35 (in its C version) is a carrier-capable aircraft. This implies that its maximum height is limited by the height of the decks/elevators of the aircraft-carrier more than by aerodynamic considerations. This is why this kind of aircraft normally have two small vertical stabilisers instead of a single big one like the Gripen. Stealth reasons can as well dictate the use of the same canted twin-tail configuration, like seen for example on the F-22:

Already this single reason explains the different location of the vertical tailplanes in respect to the engine exhaust: with a single stabiliser you want it to be mounted as rear as possible on the fuselage in order to maximise its leverarm (and minimise its size and weight); when you have two of them, they can be somewhat more freely positioned also according to other reasons, like the already mentioned stealth requirements.

Regarding the horizontal stabiliser: Well, here the difference is even bigger and it is obviously due to the fact that the F-35 has a conventional tailplane while the Gripen has a canard configuration:

Here you cannot have the exhaust "located a little inside the empennage" simply because there's no empennage.
Also other canard fighters like the Dassault Rafale in the following picture or the Eurofighter have a similar exhaust configuration like the Saab:

If the Gripen had had a conventional tailplane then it would have also been... well, on the tail! and the exhaust would have been consequently "located a little inside the empennage", just like on a F-16 for example:

All pictures from Wikipedia

I will contest the claim of carrier hangar deck height being a design factor for F-35 height. S-3 viking had a folding tail, and many carrier acft are/were taller than 5 meters, limiting height being somewhere around 5.3m. Other factors such as aerodynamics and stealth capabilities are of importance here.

I wrote "normally" not "exclusively"  Sure, they are canted mainly for stealth reasons. F-35 is indeed 4.5m high, a single vertical stabiliser would have been definitely higher than the limitations you've given. I'll update my answer with your comment, thanks.

Counter example within same manufacturer, Viggen!

@user721108: the Viggen is (was) a lifting-canard design i.e. the canard is used not only to control the airplane but also to provide lift. That implies that the main wing has to be located as backward as possible in order to give anyway a good longitudinal CG excursion and stability.

All aircraft need to have some of the vertical tail offset forward or backwards from any horizontal surface. This allows yaw control at high angle of attack, by keeping air flowing past the tails. Fighter aircraft would prefer to have a lot of the vertical tail unblanketed at high AOA, because near and post stall manuverability is key to their performance. The F-35 achieves this by having the horizontal control surfaces stick out way behind the engine exhaust and vertical tails, the Gripen achieves this by having the engine exhaust and vertical tail stick way behind the delta wing
Image from https://www.fzt.haw-hamburg.de/pers/Scholz/HOOU/AircraftDesign_9_EmpennageGeneralDesign.pdf


text:
Cascading Wings: Do they really increase lift by 300%?
Cascading Wings for Ultralights: Do they really increase lift by 333%?!?!?
The classic NACA 650-18 airfoil has a Clmax of 1.5 according to airfoiltools.com ( a modified 650-18 is used on the Zenith 701).
Add non-slatted flaps, and the Clmax jumps to about 2.2.
What if one arranges the wing in a cascading fashion as shown below? Javafoil shows the Clmax jumping to 5, that’s an increase of 333% over the plain wing!!!
Not by just adding the same planform, but dividing the original chord by 4, so the a/r ratio is 4 times the original....
So that the quadplane is 400% more efficient than the original monowing, less a quadplane inefficiency of about 50%, so that the quadplane is still 200% more efficient than the monowing(maybe).
This probably only works ( if at all ) for very slow speeds (Re 300-800k) where the form drag and induced drag is very low.
I understand Javafoil uses Xfoil, which I’m told is a robust airfoil performance prediction program and is accurate up to an AOA of +/-20 deg.
Alternately, I’m told the VLM method (XLFR) is good up to only a Clmax of 1.5, +/- 20 deg.
So…. the million dollar question is… is a Clmax of 5 realistic, or is this beyond the scope of Javafoil/xfoil, even though the AOA is only about 8 deg….?
Ultralight Design Data:
See charts and tables below.
Flaps: 20% chord, 50 deg deflection
Wing Loading:51kg/m>2
Aspect Ratio: 7
Atmospheric conditions: Standard
Wing configuration: see chart below
Gap(vertical): 50%
Stagger(horizontal): -10%
Therefore biplane ( not multiplane) lift efficiency as per the table below should be: .26/.34=76% efficiency vs mono wing (Is this correct?) ( ignore the big green arrow, it's from the source I found the table)
Reynolds #: 880k
or......
is there a glitch in the software as per the comment below:
and the Clmax is about: climax 5 / 4 wings = 1.25
given the Clmax for a monowing is 2.2, and a biplane at 50% gap is 22% less efficient, a quadplane with 4 wings can easily be 40-50% less efficient, giving a clmax of about 1.3, which is close to the clmax of 1.25 above.
So what is the likely Clmax, 5 or 1.25?

"Yes dear, I'll come to dinner just as soon as I finish troubleshooting this 'slats disagree' indicator." - Horatio Frederick Phillips

More wings didn't seem to help here  https://www.youtube.com/watch?v=TsywnRpRDUM  "7 wing biplane Gerhardt Multiplane"

Best way to reality check this is to see how many aeroplanes these days use cascading wings: none ;)

The software appears to be taking the net plan area or shadow area of the overlapping stack as its area, but is adding the individual lifts of each wing. If you add the individual areas too then the calculation should show a fall in Clmax due to interplane losses.
I'd call it a bug, however I do not know the software so perhaps it is a "feature". It depends on whether you regard your stack as one wing or four.


text:
Why aren't HLFC panels mounted on wing?
I watched The Insane Engineering of the 787 by Real Engineering. He just gave short detail about the HLFC(Hybrid Laminar Flow Control) panel and mentioned their purpose isn't available online. I found the following from flight global:

HLFC surfaces are designed to suck in the surface airflow, allowing the boundary layer to remain attached, moving the onset from laminar to turbulent flow further back along the surface, reducing overall drag.

So why they aren't mounted under the pressure side of the wing same as on the horizontal stabilizer? It would decrease the drag significantly.
My other concern, the flow is more turbulent on the suction side. Isn't it reasonable to mount an HLFC panel on the suction side rather than the pressure side of control surfaces?

You're talking about a technology which is currently tested, not a production solution.

@mins Aren't they already on 787?

Yes on the fin, not on the wing. There are studies to use HLFC on the wing, which may be in production near 2025-2030 to meet CO2 scheduled improvements requested by EU and other regulating bodies. The problem is to find a balance between additional weight from HLFC system and fuel consumption reduction, while at the same time adapting the new engines to come to the wing design.

"their purpose isn't available online": The principle of laminar flow is studied since a long time, this is not secret. See this article for more recent work.

The underside of the horizontal stablizer is (generally) the suction side, as it is producing downwards lift to keep the plane stable.
The HLFC panels shown in the video (screeshot below) are too small to make any meaningful difference to the flow, so they are most likely some sort of access doors or measuring devices. These can be see, at least on vertical stabilizer on some pictures of tails of 787-10.

Each square is supposed to be the outlet door of the suction system. Air enters through holes around the leading edge, and is rejected by a pump with this door. Better image.

Thanks! So this is a "local" system, with no functional parts outside the fins.


text:
Marshall signals history
When were airport marhall signals used for the first time? What is the history of these signals? Thank you

Do you mean history of civil aviation marshaling or aviation including military airfields?

I mean only history of civil aviation

The standard marshaling signs have been introduced in 1956 in ICAO Rules of the Air to have an international language, but someone has to explain how they were agreed, and where they were used first. Or if you are only interested in the ICAO story, let me know, I'll post an answer.

Im courious about their use for the first time, and history of these signals, who  invented this system....some information about that if u have.....thank you again!


text:
Why does the flare mode of the A321neo engage 50 feet higher than the A321ceo?
Following is taken from the operating manual of A321neo:

When passing 100 ft RA, the THS is frozen and the normal flight mode changes to flare mode as the aircraft descends to land. The flare mode is essentially a direct stick-to-elevator law without auto trim, with some damping provided by load factor and pitch rate feedback. The flare law provides full elevator authority.

Compared to 50 ft for the ceo model, why is there a difference?

Perhaps something to do with the impact of the different engines in NEO?


text:
Does adding high thrust prevent a plane from stalling?
I am convinced that fighter jets (every flying object) do stall. So from quora, Why don't fighter jets stall?
But most of the fighters have thrust:Weight ratio > 1 which means that they are not following aerodynamics at that time (during vertical climbs). You can consider them to be like rockets with propulsion system.
It suggests fighter planes don't follow aerodynamics. That means stall can be prevented using the jet power. So  what causes them to stall?
Edit: I realized my question is currently away from singularity. Based on comment, jamesqf, zeus and Robert maybe right. That quora answer might be wrong. It claims that fighter jets don't follow aerodynamics. I mean every flying object do follow it. So my question is if fighter jet has enormous power compared to their weight, will it prevent stall by a bit?
My prediction is stall only depends upon AoA. Regardless of airspeed, if AoA exceeds critical angle, stall can't be prevented (even using high thrust propulsion). Only way to prevent stall is to decrease its AoA. Are my claims correct? What if flying object relies on propulsion engine for lift (lot like missile, rocket), they keep flying and nothing hinders their speed?
Stay Safe...

So you know how stall-resistant fighters like F-16 are?

what caused you to ask this question? telling that to us might help us answer the question better. Because nearly every airplane there is - fighter or otherwise - stalls.

related: Are fly-by-wire fighters protected in AoA? and Why is the A330/A340's angle-of-attack protection disabled in alternate law, even if the AoA vanes are operating normally?

@ManuH so his question is about flight envelope protection?

@ABJX At this point I cannot say. But given stall is related to AoA and both F16 and A320 have FBW and FBW mostly comes with AoA protection, it is related.

it says, would you like to move to chat

another related Is there a standard definition of the “stall” phenomena?

Let us continue this discussion in chat.

I think your edit about supersonic vs subsonic can be a whole new question by itself (and a really interesting one).

Sure,will ask question.

@Manu H Is the updated queation understandable?

@Auberron at least for me, yes.

I think the question is based on a false premise: both fighter jets and commercial airlinere DO stall (and you can find accident reports to prove it), it's just that the pilots are trained to avoid stalling, and generally manage to do so.  And of course fighter jets have a good deal of power to pull out of stalls - just as I can use increased power to fly my Cherokee right at the edge of stall.

@jamesqf I think there is another misundertanding on definition of stall and answer should also clarify this.flying in a stall regime (above AoA) doesn't prevent from flying under control (either hovering (I'm thinking of the AV-8B) or in really high angle of attack (explored with the X-31) or more like a rocket/space shuttle on acsent)

"Most of the fighters have thrust:Weight ratio > 1" - not true. And even those that do, mostly have it at less than full weight. And even in such conditions, they rarely use it just to climb vertically: this is very inefficient. Fighters are still airplanes, and they do "follow aerodynamics".

@Manu H: AFAIK, on launch the Shuttle (or X37B, for a still active example) is not flying at all.  That is, the wings are not providing lift.  The same would be true of a fighter jet doing a vertical ascent - otherwise the jet would do a loop instead of going straight up.  (Or you'd have to use angled thrust to cancel the lift, &c)

Every aircraft can be made to stall with a combination of low speed, rear c.g. location and high load factor.
Thrust acts in the airplane's lengthwise direction. Lift acts in a mostly perpendicular direction, so whether the aircraft stalls does not depend on its thrust when lift demand exceeds the available lift capacity.
As you observe, this will not be the case in a climb. We know that lift demand is actually lower in a climb than in steady flight. So we need to look somewhere else.
The obvious case is in turning flight when the aircraft has to counteract not only gravity but also a centrifugal force. Now lift demand can grow to multiples of that in steady flight and any aircraft will readily stall if mass times normal acceleration surpasses the lift capacity of its wings. More installed thrust will only reduce the rate of energy loss in a tight circle.
Only if pitch authority is not sufficient can stall be avoided, but then the control system will not allow to trim the full angle of attack range. This could conceivably happen with a very forward center of gravity location but should place this configuration outside of certifiable limits.
As a side note: Stall depends on more than just the angle of attack.

Thanks @Peter kampf More thrust will only speed up plane in a circle?right?

"Thrust acts in the airplane's lengthwise direction". Yes, mostly, but thrust vectoring exists at least since the X-31 and is largely implemented on Sukhoi Su-27 derived fighters  and on the F-22.

@ManuH: Since vectoring happens in the nozzles, this is meant for creating pitch moments, not as a substitute to lift. Only the Harrier, the F-35B and the Yak 141 would use direct lift.

@Auberron: Speed can also be gained by diving. Thrust helps to maintain altitude or even climb in a tight circle where others would only sink in order to compensate for the massive drag created by circling.

The question perhaps may be less about the inherent characteristics of a given aircraft, and more about how the aircraft is being flown.
Some relevant points--

Given sufficient control power, a wing can be placed at the stall angle-of-attack at any airspeed.  Even if thrust is greater than weight.  Of course, in such a case, as the aircraft approached and then exceeded the stall angle-of-attack, the resulting flight path would not be anything like a straight line.
Some aircraft are designed to be maneuverable beyond the stall angle-of-attack -- e.g.  the "Cobra" maneuver.
Given the constraint of a linear flight path, the steeper the climb angle, the lower the lift force. (For more, see Does lift equal weight in a climb?)  This means that the steeper the climb angle, the lower the wing loading, if we define wing loading as lift force per unit wing area.  This means that the steeper the climb angle, the lower the unaccelerated stall speed.1  At very steep climb angles, the unaccelerated stall speed would seem to drop so low that the concept of stalling is no longer very meaningful.2  If thrust is greater than weight, a sustained vertical climb is possible.  Even if thrust is less than weight, a temporary vertical climb can be attained by exchanging kinetic energy for altitude.  If the pilot applies control inputs as needed to maintain a purely vertical flight path, then we know that no longer how low the airspeed drops, the wing must still be held at the zero-lift angle-of-attack, so the wing cannot reach the stall angle-of-attack. Of course, if the airspeed drops to zero and then the aircraft starts to tailslide backwards, the angle-of-attack at that point is arguably far beyond the stall angle-of-attack.
The same "unloading" of the wing, and resulting decrease in unaccelerated stall speed, happens in diving flight as well.  For example, if the pilot is making control inputs as needed to maintain a linear flight path, the aircraft could obviously never stall in a vertical dive, even if the pilot deployed a gigantic drogue chute that dropped the  airspeed below the normal straight-and-level stall speed.  But that doesn't mean the pilot can't stall the wing by pulling the stick back to "pull G's" to pull out of the dive.  The stall speed under heavy G-loading will be much higher than the normal straight-and-level stall speed.

Setting all theory aside, to get a feel for how a high thrust-to-weight ratio can make possible some extraordinary maneuvers, some of which involve angles-of-attack far beyond the stall angle-of-attack, search the web for videos of model airplanes engaged in "3-D" flying, such as this one.  Of course, some of the maneuvers that involve essentially zero airspeed, using the propwash to keep the control surfaces effective, would not be possible in (most if not all) jet fighter aircraft.  Nonetheless, even with no propeller, thrust-vectoring can allow for some amount of maneuvering at zero airspeed, as demonstrated by a radio-controlled model airplane in this video.
Footnotes--
1 -- For the purpose of this answer, when an aircraft is flying along a linear (not necessarily horizontal) trajectory, we'll define the unaccelerated stall speed as the speed at which the wing will reach the stall angle-of-attack if the pilot makes control inputs as needed to maintain that linear trajectory while the airspeed is slowly decreasing.  This may be an unconventional use of the term.  It is certainly not the same thing as the 1-G stall speed, unless the flight path is horizontal.
2 -- The "other side of the coin" here is that if the airspeed does decay to a very low value during a steep climb, then a modest pull on the stick might put the wing at the stall angle-of-attack while creating only a mild increase in G-loading.  In other words, if the airspeed drops very low during a steep climb, it may be easy for the pilot to accidentally cause an accelerated stall at some airspeed that is still well below the normal straight-and-level stall speed, but above the unaccelerated stall speed corresponding to the climbing linear trajectory.

Disclaimer-- I've never flown a high-perfomance jet...

A320, F-16, and paper airplane stall exactly the same way.  They are going too slow to make enough lift to hold themselves up.  They try to make more lift by increasing their angle of attack of the wing, but when the angle of attack is too much the airflow separates from the top of the wing, creating less lift and a lot more drag.
The drag makes it worse by slowing the plane down even more.  The loss of lift makes the plane fall, which makes the angle of attack of the air on the wing even greater.
The solution for all 3 is to pitch the nose down to regain speed and re-establish the proper airflow over the wing.
The problem is the amount of altitude needed to recover.  Paper airplane:  about 4 inches.
A320?  Maybe 20,000 feet.  The much greater mass of the A320 makes it much more difficult to recover.  This is why airliners try so hard not to stall.
The F-16 is much lighter than the airliner, but still would need a lot more altitude to recover than a paper airplane, or a Piper Cub.
Edits for the editor:

most fighters have a thrust to weight ratio > 1, so they are more like rockets.

Any aircraft can stall if the wing AOA exceeds the stall limit.  "Flying around like a rocket" burns up fuel very quickly and is very impractical.  Simply adding power will not necessarily break a stall.  Wing AOA must be reduced.  Unfortunately for a giant airliner, this may involve putting it into an un-recoverable dive.

Fighter planes do not follow aerodynamics

Anything moving within the earths atmosphere follows aerodynamics.  As soon as it moves, drag effects must be considered to fully understand all forces involved.

common cases of fighter jets and airliners stalling.

These events are very uncommon, and potentially disasterous.  This is why we need reliable AOA sensors and adequate safety systems to prevent this from happening.  In order to model the wing loading down to paper airplane scale, the paper airplane would have to be made of lead.

that guy seems to have more rep and badges than someone who'd ask a stupid question. see the discussion below original post.

The scale of the recovery made it interesting enough to answer, perhaps $wingloading$ would also apply.

I'm curious as to where this 20,000 foot figure comes from, it seems excessive...

@Ron Beyer if you are falling at 150 mph how long does it take to go 4 miles?  How do you stop 250 tons from falling without either exceeding G loads or re-stalling the aircraft?  A buffet or near stall recovery (by man or computer) would certainly be less, but a full blown stall/sink with the wing loading of an airliner would not be on my aviation to do list at any altitude.

@RobertDiGiovanni Here's an account of a 737 simulation from FL380 that shows recovery in about 3500 feet. Here's a video of a full stall recovery in a 737 with an FAA approved aerodynamic model, they lost about 12,000 feet I believe. Second part shows a full stall at 15,000 feet, losing probably 3,000.

Like the "you're going too slow" warning


text:
How do airports with no ATC operate?
I've heard that some airports don't have an ATC tower and nobody monitors the landings. Can someone tell me how those planes can land/takeoff safely without incidents occurring? I understand the fact that the airports without an ATC tower are small airports but wouldn't there be factors like weather which can cause accidents? So can someone please tell me how those planes can operate safely without ATC?

Not quite, but that comment did get 16 up votes :)  It's obviously more than that, but in essence, yeah, "look out the window". Seriously, though, see the quality answers below.

do you need a scheduling service when you drive to make sure you don't get too close to the next car?

I will answer this for the regulations and general procedures in the USA as laid out by the FAA, operations may vary elsewhere in the world. AOPA publishes a nice guide on how traffic flow at un-towered/un-controlled fields works and I would advise giving it a read as it covers a wide variety of scenarios. Effectively planes self announce and monitor radio traffic as they approach and depart the airfield.
Basic right of way is established in FAA FAR 91.113 and provide guidelines for operations. While some more specifics can be found in FAA FAR 91.126 and FAA FAR 91.127 relating to un-towered/un-controlled operations specifically.
Ill provide a brief example of a departure and approach (as would be heard on the radio over the Common Traffic Advisory frequency "CTAF"). You as the pilot in command are always responsible to "See and Avoid" so you should always have your heads up on approach to a field looking for traffic.

Plane is started and taxied to the run up area, checked, and lined up at the hold short line with out making any calls. You simply look around while taxing as you would when driving a car. The only exception to this is taxing on the actual runway which requires a "Piper Archer Back Taxing 05" call.
(check downwind, base, and final for incoming aircraft as you monitor the radio for calls)
(when you see its all clear) "Piper Archer taking 05 for a Northbound departure"
Enter the runway, make sure its clear, takeoff
Follow any procedures that the airport may have (noise abatement etc.)
"Piper Archer departing the pattern to the north"

Then for a basic arrival you should fly the standard traffic pattern as outlined in the AF/D for the given field.

Tune radio to CTAF and listen in if no one else is making announcements you can begin yours. For the most part everyone will make the following announcements or a similar variant there of.
"Piper archer 5 miles to the north, inbound for a landing on 05"
"Piper archer entering left downwind for 05" (General procedure calls for entering the traffic pattern on the downwind leg)
"Piper Archer turning base for 05"
"Piper archer turning final for 05"
Land
"Piper archer clear runway 05"

Some points to note. If you hear calls of others in the pattern you can still enter. Generally you want to be 1 or 2 legs behind the plane in front of you. This varies depending on what you are flying and what they are flying. For example I was landing one day in my Archer and a Seneca was inbound behind me but close, him being the heavier and far faster aircraft I let him in. Over the radio I allowed him to overtake me (I extended my downwind for him) since he was the faster plane I did not mind having some extra time to set up my approach.
On short final you should always be checking to make sure that no one pulls out onto the runway or that no one is departing. At an un-towered field dont be afraid to go around!
As Ron mentions in the comments below, there is, strictly speaking, no regulation requiring you to have a radio on board for VFR flight. That being said some older planes that lack full electrical systems also subsequently lack radios. Many have hand held units on board but again are not required to. In this case they must observe the traffic flow and enter the pattern in a safe manner, this is why you should always have your heads up looking out for aircraft doing this.

wouldn't there be factors like weather which can cause accidents?

At both big and small airports weather is handled similarly. If the conditions are VFR then a visual approach is conducted and you can avoid other aircraft by simply seeing them. The scenario above is a standard VFR arrival and approach. If the weather calls for an IFR approach and and you are in an IFR equipped aircraft and furthermore the field has an IFR approach into it (be it RNAV or GPS etc.) you may conduct an IFR approach into the field. In this case you will make calls at the proper call out points on the approach (similar to a VFR call out). Since you cant physically see the other traffic in this case radio monitoring is key.

I would've liked you to explain it for me rather than linking me to a 3rd party source

@Bhavik I have provided an example however I was simply citing my sources (FAA regulations in this case) as is common on this site. I will provide some more detail in my example.

If you fly IFR into an uncontrolled field, ATC won't clear anyone else for an instrument approach until you cancel IFR/close your flight plan (or go missed).

I put this on the other answer, but it is applicable here too... Pilots should use the radio, however there are quite a few aircraft that don't have radios. Personally I would advocate they get a hand-held, but talking on the radio is not required to land/takeoff at an uncontrolled airport.

I will add this to my answer.

Shouldn't you be using your tail-number as call-sign (and therefore show it in the example)? (Except for ultra-lights that don't have one.)

At an un-controlled field you are not required to user your tail number since no official body is listening and it is perhaps more important that you announce your type so that other pilots can determine how fast your plane is and judge their sequencing.

Dave's answer is good. I would like to provide a shorter and simpler answer here without references to external sources.
First, the radio. Get on the radio, and tell everybody three things:

Who you are
Where you are
What you are doing

For example,

N1234 is 6 miles SE, inbound for downwind runway 33

Then, you listen to others. It is as simple as that.

Now, how do pilots know which runway direction is in use, or what traffic pattern (right or left) is in use in this airport? Again, it is very simple. Either:

Observe the wind direction
Follow what everybody is doing
Refer to published charts

It is just like driving. Only instead of blinking turn signals, we use radios as pilots' intentions are more complicated than going left or right. You would also follow what every driver is doing, or follow instructions of road signs.
In both cases (driving and flying), visual see-and-avoid is utmost important. Pilots should use the radio to broadcast their intentions, and drivers should use turn signals in the same way, but that does not mean one can blindly go where they want without looking, because there will be someone not using turn signals!

Pilots should use the radio, however there are quite a few aircraft that don't have radios. Personally I would advocate they get a hand-held, but talking on the radio is not required to land/takeoff at an uncontrolled airport.

Drivers are generally required to use turn signals when turning, and hand signals where not equipped. Pilots are often not required to use a radio at non-towered fields (air carriers being one common exception), but such practice is recommended.

This only works in countries that have Unicomm or CTAF which is generally only the big ones with lots of empty space, e.g. US, Australia.

@Simon The only thing that changes in less spread out countries is that there would more likely be a specific frequency for the field (found on charts) rather than a common one.

@JonathanWalters, drivers are required to use turn signals, but half of them either forgets or remembers to use them only about the time they are starting to turn the wheel, so you can't rely on it anyway. Pilots who have radio generally remember to use it, but not all of them have it. So neither is reliable though for slightly different reason.

@JonathanWalters, so then neither is reliable, period, right?


text:
Why would the cabin crew spray the cabin before landing?
Once when I was on a plane that was about to land, the cabin crew came around and they were spraying these small canisters. I've been on many flights but it was that particular flight where they did the spray. Can someone please tell me what those spray's are?

Where were you flying from and to?

It's bug spray. http://www.cntraveler.com/stories/2016-02-19/why-flight-attendants-walk-airplane-aisles-with-bug-spray. Also here: https://www.transportation.gov/office-policy/aviation-policy/aircraft-disinsection-requirements

Maybe the passengers just smelled bad...

.....chemtrails (dun, dun, DUNNNN.......)

They spray to help disinfect and clean the cabin in case when it takes off it's not carrying a sickness on board.

They normally announce over the PA systems before spraying them, you should listen to them more.

The sprays are (usually) insecticides used to prevent the spread of invasive species and diseases.

The process of ‘disinsection’ is required under the International Health Regulations of the World Health Organization (WHO) on flights to and from certain destinations to prevent infectious and contagious diseases carried by insects and other volatile bodies. Rules established by the International Civil Aviation Organization (ICAO) require that disinsection does not injure or cause discomfort to passengers or crew. These rules permit the use of certain insecticides, which have the approval of and are recommended by the WHO based on their effectiveness and safety.

From the US dept. of Transportation

+1. I've been on flights recently where insecticide was sprayed even though the countries involved were not on the US Department of Transportation list you linked, so either the list is incomplete or airlines are spraying even where it is not required.

Why immediately before landing, rather than immediately after take-off?

@ZachLipton what country? If you read further down it says some countries require it on all flights from all countries that have zika.

@RogerLipscombe you could probably ask that as a separate se question but it would make sense to do it while on the ground in the unlikely event that someone had a bad reaction to the spray.

Air Namibia did that in the 90's on their flights between Frankfurt/Windhuk with a 747-200SP. I thought as child, or where told, that it was against air-sickness. Thinking about malaria and other possible diseases in northern Namibia this make now more sense :)

Inbound flights to NZ used to be sprayed (after landing and before disembarkation). I don't know if they still are.

@Notts90 They sprayed on a flight from Morocco to Portugal not long ago. Also one from Dubai to or from South Africa, I don't remember which direction it was.

@RogerLipscombe Why not both for extra thoroughness?

@RogerLipscombe Maybe so that they don't have to breathe the insecticides over the flight duration?

I guessed it was to prevent people breathing insecticides for the whole flight, and to allow for the possibility that someone has a reaction, but it'd be nice to see something official in the answer.

@Notts90: Well, then, why not spray just before takeoff, so that anyone having a reaction can be jettisoned immediately?

@Sean you’d also have to find a and jettison their hold luggage which could take a while and cause delays. Do it at the destination and their luggage is coming off regardless.

I was on an extremely long flight once, and the cabin crew walked up the aisles around the halfway point spraying canisters (about two in each hand) of what they said were disinfectants, required by the World Health Organization because we had so many people cooped up in a limited-air-exchange environment for so long.  The idea as explained was to prevent passenger-to-passenger disease transmission.
However, on looking it up, I find the WHO's page refer to disinfection of aircraft as being primarily about killing insects, so there may have been an error in communication.  See also this USA Today article for more information.